To elucidate the role of monocytes in the cytokine system in acute myocardial infarction (AMI), we examined the time courses of plasma concentrations and generation capacities of monocyte-related cytokines in 17 consecutive patients with uncomplicated AMI (from day 1 to 28) and in 10 control subjects. The concentrations of monocyte-related cytokines were measured by enzyme immunoassay with horseradish peroxidase. Cytokine generation capacity was evaluated by cytokine concentrations in the culture solution 24 hours after incubation of 0.5 ml whole blood with 5 micrograms lipopolysaccharide. Two distinct patterns of increases in the cytokine concentrations were noted: transient (plasma interleukin [IL]-6) and sustained (plasma macrophage colony-stimulating factor and generation capacities of IL-1 alpha, IL-6, granulocyte colony-stimulating factor, and tumor necrosis factor alpha). There was no significant increase in the concentrations of other cytokines. These results indicate that the concentrations of the monocyte-related cytokines dynamically change during the course of AMI, suggesting that they may contribute to the inflammatory and subsequent proliferative responses in AMI.